Guided projectiles in which the direction of flight is controlled by the use of transverse gas jets operated in a pulselike manner are known. Such systems can be applicable to rockets and, in general, to all types of guided projectiles. The term "guided projectile" as used herein to discuss the prior art and the system of the present invention should be understood to be applicable to all types of propelled or ballistic missiles, e.g. rockets, bombs and the like. For the purposes the present invention, however, it will be understood to be particularly directed at self-propelled short range tactical missiles.
The range of a projectile fired at a fixed or moving target is limited by various factors and, particularly, the aiming precision and dispersion at the launching site, deviations of the trajectory under the effect of atmospheric disturbances, aerodynamic imperfections in construction of the projectile and, possibly, movement of the target during the flight time of the projectile.
Because of all of these error-introducing elements, it is necessary to correct the projectile trajectory in flight to be sure that it will hit the target or come sufficiently close to perform its destructive purpose.
These trajectory corrections can be carried out over the whole flight path or only over some large or small part of it, e.g. the final phase of the flight.
To modify the projectile trajectory and, more precisely, to correct deviations from the desired trajectory, means can be provided for measuring the deviation and for generating an error signal which can operate means for applying forces to the projectile having a trajectory-correcting effect.
Detection of trajectory deviations can be performed from a sighting point which generates the correction instructions which can be transmitted by remote control to the trajectory-correcting or flight-path-correcting units on board the projectile. Alternatively, the projectile may be provided with a homing head which itself responds to deviations of the flight path from the desired trajectory to the target and produces the error signals which bring about correction of the trajectory.
Various techniques are used to modify the movement of the projectile in the aforementioned corrective manner. For example, it has been proposed to modify the flight attitude of the missile by varying its incident angle or attack angle. The resulting aerodynamic force is approximately proportional to the incident angle. The incident angle can be varied by modifying the aerodynamic-rudder positions, by the ejection of lateral gas jets, by changing the orientation of the rocket-motor gas jet or by other procedures accomplishing the same purpose.
In another approach, of a more limited utility, the movement of the missile is modified by applying to the center of gravity of the rocket a force or thrust which is transverse to its longitudinal axis and thus directly shifts the center of gravity without having to control the attitude of the projectile, i.e. the position of its axis vis-a-vis the center of gravity.
To produce such transverse forces, it has been suggested that the projectile be fitted with pyrotechnic devices capable of supplying thrusts in pulses by the ejection of gases from nozzles. This guidance method has the advantage that it applies a force to the center of gravity of the missile with a fast response to the error signal and enables the guidance of a missile without any adjustable aerodynamic control surface.
However, this system has been found to experience difficulties in that prior-art pyrotechnic devices and, in general, transverse-thrust-generating systems, which can be easily controlled and can permit trajectory correction to be made without overcorrection or complex control equipment.